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  <title>ZXing TypeScript | Decoding from camera stream</title>

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      <h1 class="title">Scan QR Code from Video Camera</h1>

      <p>
        <a class="button-small button-outline" href="../../index.html">HOME 🏡</a>
      </p>

      <p>This example shows how to scan a QR code with ZXing javascript library from the device video camera. If more
        than one video input devices are available (for example front and back camera) the example shows how to read
        them and use a select to change the input device.</p>

      <div>
        <a class="button" id="startButton">Start</a>
        <a class="button" id="resetButton">Reset</a>
      </div>

      <div>
        <video id="video" width="300" height="200" style="border: 1px solid gray"></video>
      </div>

      <div id="sourceSelectPanel" style="display:none">
        <label for="sourceSelect">Change video source:</label>
        <select id="sourceSelect" style="max-width:400px">
        </select>
      </div>

      <div style="display: table">
        <label for="decoding-style"> Decoding Style:</label>
        <select id="decoding-style" size="1">
          <option value="once">Decode once</option>
          <option value="continuously">Decode continuously</option>
        </select>
      </div>

      <label>Result:</label>
      <pre><code id="result"></code></pre>

      <p>See the <a href="https://github.com/zxing-js/library/tree/master/docs/examples/qr-camera/">source code</a> for
        this example.</p>
    </section>

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      <section class="container">
        <p>ZXing TypeScript Demo. Licensed under the <a target="_blank"
            href="https://github.com/zxing-js/library#license" title="MIT">MIT</a>.</p>
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  <script type="text/javascript" src="https://unpkg.com/@zxing/library@latest"></script>
  <script type="text/javascript">
    function decodeOnce(codeReader, selectedDeviceId) {
      codeReader.decodeFromInputVideoDevice(selectedDeviceId, 'video').then((result) => {
        console.log(result)
        document.getElementById('result').textContent = result.text
      }).catch((err) => {
        console.error(err)
        document.getElementById('result').textContent = err
      })
    }

    function decodeContinuously(codeReader, selectedDeviceId) {
      codeReader.decodeFromInputVideoDeviceContinuously(selectedDeviceId, 'video', (result, err) => {
        if (result) {
          // properly decoded qr code
          console.log('Found QR code!', result)
          document.getElementById('result').textContent = result.text
        }

        if (err) {
          // As long as this error belongs into one of the following categories
          // the code reader is going to continue as excepted. Any other error
          // will stop the decoding loop.
          //
          // Excepted Exceptions:
          //
          //  - NotFoundException
          //  - ChecksumException
          //  - FormatException

          if (err instanceof ZXing.NotFoundException) {
            console.log('No QR code found.')
          }

          if (err instanceof ZXing.ChecksumException) {
            console.log('A code was found, but it\'s read value was not valid.')
          }

          if (err instanceof ZXing.FormatException) {
            console.log('A code was found, but it was in a invalid format.')
          }
        }
      })
    }

    window.addEventListener('load', function () {
      let selectedDeviceId;
      const codeReader = new ZXing.BrowserQRCodeReader()
      console.log('ZXing code reader initialized')

      codeReader.getVideoInputDevices()
        .then((videoInputDevices) => {
          const sourceSelect = document.getElementById('sourceSelect')
          selectedDeviceId = videoInputDevices[0].deviceId
          if (videoInputDevices.length >= 1) {
            videoInputDevices.forEach((element) => {
              const sourceOption = document.createElement('option')
              sourceOption.text = element.label
              sourceOption.value = element.deviceId
              sourceSelect.appendChild(sourceOption)
            })

            sourceSelect.onchange = () => {
              selectedDeviceId = sourceSelect.value;
            };

            const sourceSelectPanel = document.getElementById('sourceSelectPanel')
            sourceSelectPanel.style.display = 'block'
          }

          document.getElementById('startButton').addEventListener('click', () => {

            const decodingStyle = document.getElementById('decoding-style').value;

            if (decodingStyle == "once") {
              decodeOnce(codeReader, selectedDeviceId);
            } else {
              decodeContinuously(codeReader, selectedDeviceId);
            }

            console.log(`Started decode from camera with id ${selectedDeviceId}`)
          })

          document.getElementById('resetButton').addEventListener('click', () => {
            codeReader.reset()
            document.getElementById('result').textContent = '';
            console.log('Reset.')
          })

        })
        .catch((err) => {
          console.error(err)
        })
    })
  </script>

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